1. Field of the Invention
This invention relates to a radio relay apparatus for use in a mobile communication system, and more particularly to a radio relay apparatus for establishing radio communication in a none sensitive area (blind zone) such as an underground area and tunnel, which has difficulty in communicating due to bad radio transmission.
2. Description of the Prior Art
There has been used a radio relay apparatus for allowing communication in a none sensitive area. The radio relay apparatus is connected to an outdoor receiving antenna through a coaxial cable, which is attached to a relay apparatus located in the none sensitive area, so as to transmit a communication signal to the relay apparatus through the coaxial cable.
In general, the coaxial cable connecting the radio relay apparatus to the receiving antenna is as long as over 100 meters in the majority of cases. The long coaxial cable exhibits larger transmission loss, resulting in consuming a large quantity of electric power. Besides, it is not easy to reduce noise figure on a receiving side.